CN117665673A - Magnetic resonance imaging apparatus - Google Patents
Magnetic resonance imaging apparatus Download PDFInfo
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- CN117665673A CN117665673A CN202311117731.XA CN202311117731A CN117665673A CN 117665673 A CN117665673 A CN 117665673A CN 202311117731 A CN202311117731 A CN 202311117731A CN 117665673 A CN117665673 A CN 117665673A
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- 238000002595 magnetic resonance imaging Methods 0.000 title claims abstract description 62
- 230000003068 static effect Effects 0.000 claims abstract description 161
- 238000003384 imaging method Methods 0.000 claims abstract description 63
- 230000007246 mechanism Effects 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 4
- 238000010586 diagram Methods 0.000 description 18
- 230000033001 locomotion Effects 0.000 description 7
- 230000008859 change Effects 0.000 description 6
- 230000005284 excitation Effects 0.000 description 5
- 230000036962 time dependent Effects 0.000 description 4
- 206010009244 Claustrophobia Diseases 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 208000019899 phobic disease Diseases 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 229910001275 Niobium-titanium Inorganic materials 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 229910052734 helium Inorganic materials 0.000 description 2
- 239000001307 helium Substances 0.000 description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- RJSRQTFBFAJJIL-UHFFFAOYSA-N niobium titanium Chemical compound [Ti].[Nb] RJSRQTFBFAJJIL-UHFFFAOYSA-N 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000005347 demagnetization Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000002123 temporal effect Effects 0.000 description 1
- 230000001052 transient effect Effects 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
- G01R33/3815—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets with superconducting coils, e.g. power supply therefor
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/30—Sample handling arrangements, e.g. sample cells, spinning mechanisms
- G01R33/307—Sample handling arrangements, e.g. sample cells, spinning mechanisms specially adapted for moving the sample relative to the MR system, e.g. spinning mechanisms, flow cells or means for positioning the sample inside a spectrometer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/32—Excitation or detection systems, e.g. using radio frequency signals
- G01R33/34—Constructional details, e.g. resonators, specially adapted to MR
- G01R33/34007—Manufacture of RF coils, e.g. using printed circuit board technology; additional hardware for providing mechanical support to the RF coil assembly or to part thereof, e.g. a support for moving the coil assembly relative to the remainder of the MR system
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/385—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using gradient magnetic field coils
- G01R33/3858—Manufacture and installation of gradient coils, means for providing mechanical support to parts of the gradient-coil assembly
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/387—Compensation of inhomogeneities
- G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
- G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
- G01R33/387—Compensation of inhomogeneities
- G01R33/3875—Compensation of inhomogeneities using correction coil assemblies, e.g. active shimming
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/543—Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56563—Correction of image distortions, e.g. due to magnetic field inhomogeneities caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
- G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
- G01R33/48—NMR imaging systems
- G01R33/54—Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
- G01R33/56—Image enhancement or correction, e.g. subtraction or averaging techniques, e.g. improvement of signal-to-noise ratio and resolution
- G01R33/565—Correction of image distortions, e.g. due to magnetic field inhomogeneities
- G01R33/56509—Correction of image distortions, e.g. due to magnetic field inhomogeneities due to motion, displacement or flow, e.g. gradient moment nulling
Abstract
The present invention relates to a magnetic resonance imaging apparatus capable of performing imaging in an imaging space in accordance with an operation of a subject and a free posture of the subject. A magnetic resonance imaging apparatus according to one embodiment includes: a static magnetic field magnet including a superconducting coil, the static magnetic field magnet generating a static magnetic field having a static magnetic field distribution in an open area outside the superconducting coil; a control circuit for adjusting the static magnetic field distribution; and a reconstruction processing circuit that generates a magnetic resonance image based on magnetic resonance signals emitted from a subject having at least a part of an open region disposed outside the superconducting coil.
Description
The present application is based on Japanese patent application 2022-141428 (application day: 9/6 of 2022) and enjoys priority of the application. This application is incorporated by reference into this application in its entirety.
Technical Field
Embodiments disclosed in the present specification and drawings relate to a magnetic resonance imaging apparatus.
Background
The magnetic resonance imaging apparatus is an imaging apparatus that excites nuclear spins of a subject placed in a static magnetic field with a Radio Frequency (RF) signal of larmor Frequency, and reconstructs a magnetic resonance signal (MR (Magnetic Resonance) signal) generated from the subject in response to the excitation to generate an image.
Many magnetic resonance imaging (MRI: magnetic Resonance Imaging) apparatuses have a structure called a gantry (gantry) in which a cylindrical space (the space is called a bore) is formed. A subject (for example, a patient) lying on the top plate is photographed while being carried into a cylindrical space. A cylindrical static magnetic field magnet, a cylindrical gradient magnetic field coil, and a cylindrical transmitting/receiving coil (i.e., WB (Whole Body) coil) are housed in the gantry. In many of such magnetic resonance imaging apparatuses in the past, the static field magnet, the gradient magnetic field coil, and the transmitting/receiving coil have a cylindrical shape, and therefore, such a magnetic resonance imaging apparatus will be hereinafter referred to as a cylindrical magnetic resonance imaging apparatus.
In a cylindrical magnetic resonance imaging apparatus, imaging is performed in a closed space in a hole, and thus, it is sometimes difficult to perform imaging of a part of patients such as claustrophobia.
In contrast, the following magnetic resonance imaging apparatuses have been proposed and developed: the static field magnet and the gradient field coil are formed in a flat plate shape, and for example, a subject such as a patient is imaged in an open space sandwiched between two flat plate-shaped static field magnets. Such a magnetic resonance imaging apparatus will be referred to as a planar open magnetic resonance imaging apparatus (or simply as an open magnetic resonance imaging apparatus) hereinafter. In an open magnetic resonance imaging apparatus, since imaging is performed in an open space, a patient suffering from claustrophobia can be imaged.
On the other hand, in the case of a cylindrical magnetic resonance imaging apparatus, imaging is performed in a narrow region where the magnetic field uniformity in the bore is high, whereas in the case of an open magnetic resonance imaging apparatus, the position of the subject with respect to the static field magnet is not necessarily fixed because the subject is imaged in a relatively wide open space.
The imaging of the magnetic resonance imaging apparatus requires a relatively long time and is exposed to a noisy environment. Therefore, for example, when a child, an elderly person, or the like is photographed in a wide open space, the possibility of motion during photographing increases, and a risk of artifacts due to body movement occurs.
In addition, depending on the condition of the patient, it may be difficult to sit down on the top plate. In this case, it is required to be able to take a photograph in a free posture according to the condition of the patient. However, in order to meet such a requirement, it is necessary to be able to freely adjust the position and range of the imaging region according to the condition of the patient.
Disclosure of Invention
One of the problems to be solved by the embodiments disclosed in the present specification and the drawings is that an open magnetic resonance imaging apparatus can perform imaging in accordance with the motion of a subject and the free posture of the subject in an imaging space. However, the problems to be solved by the embodiments disclosed in the present specification and the drawings are not limited to the above-described problems. The problems associated with the effects of the configurations described in the embodiments described below may be located as other problems.
A magnetic resonance imaging apparatus according to one embodiment includes: a static magnetic field magnet including a superconducting coil, the static magnetic field magnet generating a static magnetic field having a static magnetic field distribution in an open area outside the superconducting coil; a control circuit for adjusting the static magnetic field distribution; and a reconstruction processing circuit that generates a magnetic resonance image based on magnetic resonance signals emitted from a subject having at least a part of an open region disposed outside the superconducting coil.
With the above configuration, in the open magnetic resonance imaging apparatus, imaging can be performed in accordance with the motion of the subject and the free posture of the subject in the imaging space.
Drawings
Fig. 1 is a diagram showing a first configuration example of a magnetic resonance imaging apparatus according to an embodiment.
Fig. 2 is a diagram showing a second configuration example of the magnetic resonance imaging apparatus according to the embodiment.
Fig. 3 is a diagram showing an example of the structure of a static field magnet.
Fig. 4 is a diagram schematically showing the configuration of a superconducting coil and a static magnetic field power supply connected to the superconducting coil, which are provided in the magnetic resonance imaging apparatus according to the embodiment.
Fig. 5 is a diagram showing an exemplary configuration of a static field magnet having three superconducting coils.
Fig. 6 is a diagram showing a configuration example of a magnetic resonance imaging apparatus according to the first embodiment.
Fig. 7 is a diagram schematically showing a change in the position of the imaging region when the respective currents supplied to the two superconducting coils are changed.
Fig. 8 is a diagram schematically showing a time-dependent pattern of current with respect to the superconducting coil.
Fig. 9 is a diagram showing a configuration example of a magnetic resonance imaging apparatus according to a second embodiment.
Reference numerals illustrate:
1 magnetic resonance imaging apparatus
10. Static magnetic field magnet
20. Local coil
40. Static magnetic field power supply
42. Control circuit
60. Gradient magnetic field coil
62 RF coil
70. Magnetic body
72. Driving mechanism
101. 102, 103 superconducting coils
Detailed Description
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(first embodiment)
Fig. 1 is a diagram showing a first configuration example of an open magnetic resonance imaging apparatus 1 according to the embodiment. As illustrated in fig. 1, the magnetic resonance imaging apparatus 1 includes, for example, two static field magnets 10 in a circular flat plate shape (in other words, a thin cylindrical shape).
The static field magnets 10 are arranged such that the central axis of the static field magnet 10, that is, the axis passing through the center of the circle on both end surfaces of the cylindrical shape is parallel to the ground, for example. The two static field magnets 10 are disposed so as to sandwich the subject. With this arrangement of the static field magnets 10, a magnetic field is formed in the open space between the two static field magnets 10. The subject is imaged in this open space, for example, in a standing position.
Fig. 2 is a diagram showing a second configuration example of the open type magnetic resonance imaging apparatus 1. Fig. 1 shows an example of a structure for photographing a subject in a standing position, while fig. 2 shows an example of a structure for photographing a subject in a lying position lying on a top plate 80 of a bed 81. In the case of photographing a subject in a prone position, as shown in fig. 2, the two static field magnets 10 are arranged such that the central axis is in the vertical direction, for example, one static field magnet 10 is arranged below the top plate 80 and the other static field magnet 10 is arranged above the top plate 80.
As shown in fig. 1 and 2, in the imaging using the static field magnet 10 according to the embodiment, the subject can be imaged in the open magnetic field space, and thus, even a patient suffering from claustrophobia, for example, can be imaged.
In fig. 1 and 2, the case where the subject is imaged in the open area outside the static field magnet 10 including the superconducting coil is shown, but the imaging may be performed in a state where at least a part of the subject is placed in the open area outside the superconducting coil.
Fig. 3 is a diagram showing an example of the structure of the static field magnet 10. Each static field magnet 10 incorporates a superconducting coil 101. The static field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power source 40 (see fig. 4, etc.) to the superconducting coil 10 in the excitation mode, and then turns off the static magnetic field power source 40 if the mode is switched to the permanent current mode. When the mode is switched to the permanent current mode, the static field magnet 10 continuously generates a large static field for a long period of time, for example, for 1 year or longer.
On the other hand, the operation mode may be one in which the current is continuously applied from the static magnetic field power supply to the superconducting coil 101 even during the operation period including the shooting without cutting off the static magnetic field power supply 40. This operation mode is referred to as a control current mode.
In the magnetic resonance imaging apparatus 1 according to the embodiment, the magnetic resonance imaging apparatus 1 is configured so as to be adjustable or changeable without fixing the position and shape of the static magnetic field distribution of the imaging region R, as schematically indicated by arrows in fig. 3, in both the permanent current mode and the control current mode.
Fig. 4 schematically shows the structure of a superconducting coil 101 included in the magnetic resonance imaging apparatus 1 according to the embodiment and a static magnetic field power source 40 connected to the superconducting coil 101. As shown in the lower diagram of fig. 4, superconducting coil 101 according to the embodiment is divided into a plurality of segments.
In the example shown in fig. 4, superconducting coil 101 is configured by dividing it into 9 segments 101a, 101b, 101c, 101d, 101e, 101f, 101g, 101h, and 101 i.
In other words, the superconducting coil 101 is divided into a plurality of segments, and each segment has a structure having a superconducting sub-coil (hereinafter, simply referred to as a sub-coil) independent of the other segments.
The sub-coils of each segment may have a multi-core structure in which a superconducting wire such as niobium-titanium (Nb-Ti) or a rare earth-based or bismuth-based high temperature superconducting wire is formed into a plurality of filaments or strips and a normal electric base material such as copper is embedded therein. The superconducting coil 101, which is an aggregate of the plurality of segments, is immersed in, for example, a liquid helium container (not shown) filled with liquid helium.
The sub-coils of each segment may be connected to the static magnetic field power source 40 in parallel with each other, and may be configured to receive independent current supplies from the static magnetic field power source 40. By independently controlling the magnitude and direction of the current value supplied from the static magnetic field power source 40 to each sub-coil, or the on/off of the current, the shape of the static magnetic field distribution such as the intensity of the static magnetic field generated by the superconducting coil 101, the magnitude and position of the static magnetic field distribution, and the like can be adjusted to a desired state.
As described above, one of the sub-coils of the plurality of segments included in the superconducting coil 101 may be connected in parallel with the static magnetic field power supply 40, while several of the sub-coils of the other segment may be connected in series, and both ends of the plurality of sub-coils connected in series may be connected to the static magnetic field power supply 40. In this case, the number of groups of the plurality of sub-coils connected in series may be one or two or more.
In the example shown in fig. 4, currents are supplied from the static magnetic field power supply 40 to the 9 segments 101a, 101b, 101c, 101d, 101e, 101f, 101g, 101h, and 101i constituting the superconducting coil 101 using 6 feeder lines. In this case, for example, the four segments 101a, 101b, 101c, and 101d may be configured to supply independent currents in parallel using 4 power supply lines. On the other hand, segments 101e and 101f are connected in series to form a first series group, and three segments 101g, 101h, 101i are also connected in series to form a second series group. The first series group and the second series group may be supplied with current by using the remaining 2 power supply lines of the static magnetic field power supply 40.
The magnitude and direction of the current supplied from the static magnetic field power source 40 to each segment of the superconducting coil 101 may be controlled by the static magnetic field power source 40 itself or by a control circuit 42 (see fig. 6) connected to the static magnetic field power source 40.
Fig. 3 and 4 show a configuration in which the static field magnet 10 includes one superconducting coil 101, but the static field magnet 10 may include a plurality of superconducting coils. Fig. 5 shows an exemplary configuration of the static field magnet 10 including three superconducting coils 101, 102, 103. In the example shown in fig. 5, three circular superconducting coils 101, 102, 103 having different diameters are coaxially arranged.
Each superconducting coil 101, 102, 103 is divided into 1 or more segments. In the example shown in fig. 5, the superconducting coil 101 is divided into 9 segments, the superconducting coil 102 is divided into 8 segments, and the superconducting coil 103 is divided into 2 segments, as in fig. 4.
Not only the superconducting coil 101 but also the magnitude and direction of the current value supplied to the sub-coils of each of the other two superconducting coils 102 and 103, or the on and off of the current, can be controlled independently, whereby the intensity of the static magnetic field formed on the whole static magnetic field magnet 10, the magnitude and position of the static magnetic field distribution, and the shape of the static magnetic field distribution can be adjusted with a higher degree of freedom.
Fig. 6 is a diagram showing a configuration example of the magnetic resonance imaging apparatus 1 according to the first embodiment in which the static field magnet 10 shown in fig. 5 is disposed on the upper side and the lower side with the subject P lying therebetween. An imaging region R (or FOV (Field of View)) is formed between the two static field magnets 10.
The magnetic resonance imaging apparatus 1 shown in fig. 6 includes, in addition to the two static field magnets 10 described above, a top plate 80 on which the subject P lies, a local coil 20 disposed close to the subject, a gradient magnetic field coil 60, and a RF (Radio Frequency) coil 62.
The magnetic resonance imaging apparatus 1 further includes a static magnetic field power supply 40, a control circuit 42, an imaging condition setting circuit 50, a sequence controller 51, a gradient magnetic field power supply 52, a transmission circuit 53, a reception circuit 54, and a reconstruction processing circuit 55.
The imaging condition setting circuit 50 sets imaging conditions such as the type of pulse sequence and the values of various parameters input via a user interface, not shown, to the sequence controller 51.
The sequence controller 51 drives the gradient magnetic field power supply 52 and the transmission circuit 53, respectively, based on the set imaging conditions, thereby scanning the subject. The gradient magnetic field power supply 52 applies a gradient magnetic field current to the gradient magnetic field coils 60 based on a drive signal from the sequence controller 51.
The transmission circuit 53 generates an RF pulse based on the drive signal from the sequence controller 51, and applies the RF pulse to the RF coil 62. A MR (Magnetic Resonance) signal emitted from the subject P in response to the application is received by the local coil 20. The MR signals received by the local coil 20 are converted from analog signals to digital signals by the receiving circuit 54. The MR signals converted into digital signals are supplied as k-space data to the reconstruction processing circuit 55. The reconstruction processing circuit 55k performs a reconstruction process such as an inverse fourier transform process on the spatial data to generate a magnetic resonance image.
As described above, the static field power supply 40 supplies currents to the superconducting coils 101, 102, 103 of the upper and lower static field magnets 10, respectively, under the control of the control circuit 42. In fig. 6, in order to avoid the complexity of the drawing, it is illustrated that the current is supplied to the superconducting coils 101, 102, 103 by 1 power supply line, but the current may be supplied to the superconducting coils 101, 102, 103 by a plurality of power supply lines, thereby performing independent current control for the sub-coils of a plurality of segments in the superconducting coils 101, 102, 103, respectively.
As described above, the control circuit 42 can adjust the static magnetic field distribution by independently controlling at least one of the direction and the magnitude of the current flowing to the segments of the superconducting coils 101, 102, and 103.
For example, in all or any of the superconducting coils 101, 102, and 103, the plurality of segments may be classified into a first group and a second group, and the static magnetic field distribution may be adjusted by flowing a reverse current through one or more first sub-coils belonging to the first group and one or more second sub-coils belonging to the second group.
Alternatively, instead of or in addition to the independent control of the currents between the segments, the static magnetic field distribution can be adjusted by independently controlling at least one of the direction and the magnitude of the currents flowing through the superconducting coils 101, 102, 103 among the superconducting coils 101, 102, 103.
The operation mode of the current supplied from the static magnetic field power supply 40 to the superconducting coils 101, 102, 103 may be a permanent current mode or a control current mode.
Here, the permanent current mode is an operation mode of a current that continuously flows through the superconducting coils 101, 102, 103 in a state where the static magnetic field power supply 40 is turned off after the current applied to the superconducting coils 101, 102, 103 is increased from zero to a predetermined value. The transient operation mode in which the current applied to the superconducting coils 101, 102, 103 is increased from zero to a predetermined value is referred to as an excitation mode.
The direction and magnitude of the current flowing through the superconducting coils 101, 102, 103 and each segment in the permanent current mode are predetermined at the start of the excitation mode, and are fixed after the transition to the permanent current mode.
On the other hand, the control current mode is an operation mode in which current is continuously applied from the static magnetic field power supply to the superconducting coil 101 even during an operation period including shooting without cutting off the static magnetic field power supply 40. The direction and magnitude of the current flowing through the superconducting coils 101, 102, 103 and each segment in the control current mode can be changed at a desired timing before or during shooting.
Regarding the operation mode of the current supplied from the static magnetic field power supply 40 to the superconducting coils 101, 102, 103, one of the permanent current mode and the control current mode may be assigned to all the superconducting coils 101, 102, 103 and all the segments, or the permanent current mode and the control current mode may be mixed between the plurality of superconducting coils 101, 102, 103 or between the plurality of segments.
As described above, the static magnetic field distribution can be adjusted by controlling the current of the static magnetic field power supply 40 by the control circuit 42. Further, by adjusting the static magnetic field distribution, that is, changing the shape and position of the static magnetic field distribution, at least one of the position of the imaging region of the subject, the range of the imaging region of the subject, and the intensity of the static magnetic field can be adjusted.
The control circuit 42 may acquire imaging conditions from the imaging condition setting circuit 50 and adjust the static magnetic field distribution based on the acquired imaging conditions. In this case, the acquired imaging conditions include, for example, at least one of the position of the imaging region of the subject, the range of the imaging region of the subject, and the intensity of the static magnetic field, and the control circuit 42 determines the currents to be supplied to the respective segments of the superconducting coils 101, 102, 103 to obtain a desired static magnetic field distribution based on these imaging conditions.
The control circuit 42 holds a lookup table in which imaging conditions such as the position of the imaging region, the range of the imaging region of the subject, and the intensity of the static magnetic field are associated with currents supplied to the respective segments of the superconducting coils 101, 102, 103 for obtaining the static magnetic field distribution corresponding to the imaging conditions. The control circuit 40 can determine the current to be supplied to each segment according to the imaging conditions set in the imaging condition setting circuit 50 by referring to the lookup table.
Fig. 7 is a diagram schematically showing a change in the position of the imaging region R when parameters such as the current of the static magnetic field power supply and the sectional area of the segment of the superconducting coil are changed as an example of adjustment of the static magnetic field distribution. For convenience of explanation, fig. 7 illustrates a configuration in which the upper static field magnet 10 is removed from the configuration shown in fig. 6.
Fig. 7 is a diagram schematically showing a change in the position of the imaging region R corresponding to the static magnetic field distribution when the sectional area Sa and the sectional area Sb are changed when the currents supplied to the superconducting coils 101 and 102 are the currents Ia and Ib and the sectional areas of the segments of the superconducting coils 101 and 102 are the sectional area Sa and the sectional area Sb in the case where the static magnetic field magnet 10 has two superconducting coils 101 and 102.
In the graph shown on the right side of fig. 7, a combination of values of the cross-sectional area Sa and the cross-sectional area Sb is indicated by a white quadrangle, and the position of the imaging region R corresponding to the combination is indicated by a black circle. Here, the position of the imaging region R is set to a distance D from the upper end of the static field magnet 10 (or the superconducting coils 101, 102) to the center of the imaging region R. From this graph, it is understood that the position of the imaging region R can be changed by changing the values of the cross-sectional area Sa and the cross-sectional area Sb.
In addition, even if the current Ia and the current Ib are changed instead of changing the cross-sectional area Sa and the cross-sectional area Sb, the position of the imaging region R can be changed.
The above is an example of adjustment of the static magnetic field distribution, and the static magnetic field distribution can be adjusted by adjusting the current of the static magnetic field power supply 40 and other parameters than the sectional area of the segment of the superconducting coil.
As described above, by adjusting the static magnetic field distribution, for example, in the imaging space between the two static magnetic field magnets 10, imaging can be performed even when the subject is in motion. In addition, imaging according to the free posture of the subject can also be performed.
However, in order to determine the rate of increase or decrease of the current applied to the superconducting coils 101, 102, 103 in the permanent current mode, that is, the time-varying pattern of the current increasing from zero to a predetermined permanent current, or the time-varying pattern of the current decreasing from the predetermined permanent current to zero during demagnetization, various parameters need to be considered.
In the control current mode, various parameters are also required to be considered when determining a time-dependent change pattern of current when current is applied to or reduced from the superconducting coils 101, 102, 103 while maintaining the superconducting state.
Fig. 8 is a diagram schematically showing a pattern of change with time of current with respect to the superconducting coils 101, 102, 103 including when exciting and when demagnetizing. In the example of the pattern of the temporal change in current shown in fig. 8, at time t 0 Excitation is started at time t 0 By time t 1 During which the current increases from zero to current I (1), at time t 1 By time t 2 During the period of (2), the current is maintained at the current I (1), at the time t 2 By time t 3 During which the current increases further from the current I (1) to the current I (2), at a time t 3 By time t 4 During the period of (2), the current is maintained at the current I (2), at the time t 4 By time t 5 During which the current decreases from current I (2) to current I (3), at time t 5 By time t 6 During the period of (2), the current is maintained at the current I (3), at the time t 6 By time t 7 The current decreases from current I (3) to current zero.
Here, the time-dependent pattern of the current of the static field power supply 40 for exciting the static field magnet 10 (or for increasing the intensity of the static field) and the time-dependent pattern of the current of the static field power supply 40 for demagnetizing the static field magnet 10 (or for decreasing the intensity of the static field) are determined based on at least one of the shape of the static field distribution to be realized, the intensity of the static field to be realized, the temperature of the superconducting coil 101 or the like, the empirical magnetic field of the superconducting coil 101 or the like, and the cooling performance for cooling the superconducting coil 101.
Here, regarding the temperature of the superconducting coils 101 and the like, data of a temperature sensor provided adjacent to each superconducting coil 101 and the like may be acquired as magnet monitor information. Parameters such as the shape of the static magnetic field distribution to be achieved, the intensity of the static magnetic field to be achieved, and the cooling performance may be given to the control circuit 42 in advance. The shape of the static magnetic field distribution to be realized and the intensity of the static magnetic field to be realized may be determined based on the imaging conditions set by the imaging condition setting circuit 50.
(second embodiment)
Fig. 9 is a diagram showing a configuration example of the magnetic resonance imaging apparatus 1 according to the second embodiment. The first difference from the first embodiment (see fig. 6) is that the magnetic resonance imaging apparatus 1 of the second embodiment includes a magnetic body 70 for adjusting the distribution of the static magnetic field. The magnetic body 70 is a member including a magnetic body such as iron or nickel. The magnetic body 70 is disposed between the static field magnet 10 and the top plate 80, for example. In addition, the magnetic body 70 may be provided in a vacuum vessel called a cryostat. The magnetic body 70 may be configured as a coil.
The magnetic body 70 is moved, for example, in the longitudinal direction or the short side direction of the top plate 80 by the driving mechanism 72 under the control of the control circuit 42. By moving the magnetic body 70, the shape of the static magnetic field distribution and the intensity of the static magnetic field can be adjusted, and as a result, the size and position of the imaging region R can be adjusted.
The second difference from the first embodiment is that the magnetic resonance imaging apparatus 1 of the second embodiment moves at least one of the gradient magnetic field coil 60, the RF coil 62, and the top plate 80 relative to the static magnetic field magnet 10. Similar to the magnetic body 70 described above, the gradient magnetic field coil 60, the RF coil 62, or the top plate 80 can be moved, for example, in the longitudinal direction or the short side direction of the top plate 80 by the driving mechanism 72 under the control of the control circuit 42. By moving these, the shape of the static magnetic field distribution and the intensity of the static magnetic field can be adjusted, and as a result, the size and position of the imaging region R can be adjusted.
As described above, in the magnetic resonance imaging apparatus 1 according to the second embodiment, the size and position of the imaging region R can be adjusted, and imaging can be performed even when the subject is in motion in the imaging space between the two static field magnets 10. In addition, imaging according to the free posture of the subject can also be performed.
(third embodiment)
In the magnetic resonance imaging apparatus 1 (fig. 6) of the first embodiment or the magnetic resonance imaging apparatus 1 (fig. 9) of the second embodiment, the two static field magnets 10 facing each other are provided, and the subject is imaged in a space sandwiched between the two static field magnets 10.
In contrast, the third magnetic resonance imaging apparatus 1 is configured to include only one static field magnet 10 of the two static field magnets 10. For example, the magnetic resonance imaging apparatus 1 of the third embodiment may be configured such that the static field magnet 10 on the upper side of the top plate 80 is removed from the configuration of the magnetic resonance imaging apparatus 1 of the first and second embodiments shown in fig. 6 and 9. In the third embodiment, the static field magnet is configured to have only the static field magnet 10 disposed below the top plate 80. The magnetic resonance imaging apparatus 1 according to the third embodiment can also obtain the same effects as those of the first and second embodiments.
According to at least one embodiment described above, in the open magnetic resonance imaging apparatus, imaging according to the motion of the subject and the free posture of the subject in the imaging space can be performed.
Although several embodiments are described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other modes, and various omissions, substitutions, modifications, and combinations of the embodiments can be made without departing from the spirit of the invention. These embodiments and modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and equivalents thereof.
Claims (12)
1. A magnetic resonance imaging apparatus is provided with:
a static magnetic field magnet including a superconducting coil, the static magnetic field magnet generating a static magnetic field having a static magnetic field distribution in an open area outside the superconducting coil;
a control circuit for adjusting the static magnetic field distribution; and
a reconstruction processing circuit that generates a magnetic resonance image based on magnetic resonance signals emitted from a subject, at least a part of which is disposed in an open area outside the superconducting coil.
2. The magnetic resonance imaging apparatus of claim 1, wherein,
the superconducting coil is constructed by being divided into a plurality of segments,
the control circuit independently controls the current flowing through the superconducting coils for each of the segments, thereby adjusting the static magnetic field distribution.
3. The magnetic resonance imaging apparatus of claim 2, wherein,
the control circuit adjusts the static magnetic field distribution by controlling at least one of the direction and the magnitude of the current flowing through the superconducting coil independently for each segment.
4. The magnetic resonance imaging apparatus of claim 2, wherein,
the superconducting coils have at least a first superconducting coil belonging to a first group of segments and a second superconducting coil belonging to a second group of segments,
the control circuit adjusts the static magnetic field distribution by making a direction of a first current flowing through the first superconducting coil and a direction of a second current flowing through the second superconducting coil opposite to each other and controlling magnitudes of the first current and the second current independently.
5. The magnetic resonance imaging apparatus of claim 2, wherein,
and a static magnetic field power supply for applying a current to the superconducting coil,
the control circuit controls the static magnetic field distribution by a permanent current mode in which a current continuously flows through the superconducting coil in a state where the static magnetic field power supply is turned off after a current applied to the superconducting coil is increased to a predetermined value.
6. The magnetic resonance imaging apparatus of claim 2, wherein,
and a static magnetic field power supply for applying a current to the superconducting coil,
the control circuit adjusts a current flowing through the superconducting coil in a state where the static magnetic field power supply is connected to the superconducting coil, thereby controlling the static magnetic field distribution.
7. The magnetic resonance imaging apparatus of claim 2, wherein,
and a static magnetic field power supply for applying a current to the superconducting coil,
the control circuitry may be configured to control the operation of the control circuitry,
for a first superconducting coil belonging to a first group of segments among the plurality of segments, controlling the static magnetic field distribution by a permanent current mode in which a current continuously flows in the first superconducting coil in a state in which the static magnetic field power supply is turned off after a current applied to the first superconducting coil is increased to a prescribed value,
on the other hand, in the second superconducting coil belonging to the second segment other than the first segment of the plurality of segments, the static magnetic field distribution is controlled by adjusting the current flowing through the second superconducting coil in a state where the static magnetic field power supply is connected to the second superconducting coil.
8. The magnetic resonance imaging apparatus of claim 1, wherein,
the control circuit adjusts at least one of a position of an imaging region of the subject, a range of the imaging region of the subject, and an intensity of the static magnetic field by adjusting the static magnetic field distribution.
9. The magnetic resonance imaging apparatus of claim 8, wherein,
further comprises a shooting condition setting circuit for setting shooting conditions,
the imaging condition includes at least one of a position of an imaging region of the subject, a range of the imaging region of the subject, and an intensity of the static magnetic field,
the control circuit adjusts the static magnetic field distribution based on the set imaging condition.
10. The magnetic resonance imaging apparatus of claim 1, wherein,
and a static magnetic field power supply for applying a current to the superconducting coil,
the control circuit determines a time-varying pattern of a current of the static magnetic field power supply for exciting the static magnetic field magnet and a time-varying pattern of a current of the static magnetic field power supply for demagnetizing the static magnetic field magnet based on at least one of the static magnetic field distribution, the intensity of the static magnetic field, the temperature of the superconducting coil, the empirical magnetic field of the superconducting coil, and the cooling performance of the superconducting coil.
11. The magnetic resonance imaging apparatus according to claim 1, further comprising:
a magnetic body for adjusting the static magnetic field distribution; and
a driving mechanism for moving the magnetic body,
the control circuit controls the driving mechanism to relatively move the magnetic body with respect to the static field magnet, thereby adjusting the static field distribution.
12. The magnetic resonance imaging apparatus according to claim 1, further comprising:
a gradient magnetic field coil for applying a gradient magnetic field to the subject;
an RF coil that applies a high-frequency magnetic field to the subject;
a top plate on which the subject is lying; and
a driving mechanism for moving at least one of the gradient magnetic field coil, the RF coil, and the top plate,
the control circuit controls the driving mechanism to relatively move at least one of the gradient magnetic field coil, the RF coil, and the top plate with respect to the static magnetic field magnet, thereby adjusting the static magnetic field distribution.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2022-141428 | 2022-09-06 | ||
| JP2022141428A JP2024036888A (en) | 2022-09-06 | 2022-09-06 | magnetic resonance imaging device |
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| CN117665673A true CN117665673A (en) | 2024-03-08 |
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| CN202311117731.XA Pending CN117665673A (en) | 2022-09-06 | 2023-08-31 | Magnetic resonance imaging apparatus |
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| Country | Link |
|---|---|
| US (1) | US20240077556A1 (en) |
| EP (1) | EP4345474A2 (en) |
| JP (1) | JP2024036888A (en) |
| CN (1) | CN117665673A (en) |
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2022
- 2022-09-06 JP JP2022141428A patent/JP2024036888A/en active Pending
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- 2023-08-22 US US18/453,372 patent/US20240077556A1/en active Pending
- 2023-08-31 CN CN202311117731.XA patent/CN117665673A/en active Pending
- 2023-08-31 EP EP23194660.9A patent/EP4345474A2/en active Pending
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| JP2024036888A (en) | 2024-03-18 |
| EP4345474A2 (en) | 2024-04-03 |
| US20240077556A1 (en) | 2024-03-07 |
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